1. Field of the Invention
The present invention relates to the recovery of mercury from aqueous streams. More particularly, the present invention relates to improvements in the recovery of mercury from aqueous streams by filtration through polytetrafluoroethylene membrane filters.
2. Description of the Prior Art
The mercury type electrolytic cell for the production of chlorine and caustic has been used primarily because of the high purity caustic soda which is produced. Recently, it has been found, however, the loss of mercury from the effluent streams issuing from these electrolytic cells has created ecological problems. Furthermore, the loss of mercury is a costly expenditure in the caustic and chlorine producing plants. Accordingly it is imperative that means be found for the removal of mercury and/or other heavy metal ions from liquid streams. It is generally accepted procedure to precipitate heavy metals from solution and collect them on a precoated filter medium. This filter medium becomes contaminated with insolubles and must be removed to allow for further filtration. Furthermore, it is desirable to recover the mercury to derive some economic benefits from the filtration process. A number of patents among which are U.S. Pat. Nos. 3,843,570 and 3,258,398 teach the use of polytetrafluoroethylene membranes as filtration mediums. There is, however, no teaching that such membranes could be employed to filter out finely divided mercuric sulfide or metallic mercury from plant effluent streams.